The present invention relates generally to a device and method for adjusting a force applied to a movable element such as a platform.
Scissors-type linkages are used in many devices and machines for providing movable characteristics, e.g. in lifting devices such as liftable platforms. The scissors-type linkage allows for lifting a platform into an upper, open or extended position starting from a lower, close or retracted position in which the platform can come very close to a base or the floor or can even contact one of those.
A movable element such as a liftable platform which is connected, e.g. to a base, a floor, an operation deck or the frame of a machine such as a printing machine, can be moved, e.g. raised, by the operator himself, by a driving device such as a motor or by the assistance of an energy-recycling mechanism or device.
The force which is applied to the movable element has to be adjusted based on the weight of the movable element, the weight of the scissors-type linkage and perhaps on the weight of a load or an operator in the case where the scissors-type linkage is used to lift or hold goods or operators. If no additional loads are present, the force only has to compensate or exceed the gravitational and frictional forces of the mechanism itself.
It is advantageous to use an energy-recycling device such as a gas spring for moving or raising the element. The energy which becomes free when the element is moved in its lower position can then be stored in the energy-recycling device, e.g. in the compression of a gas in the gas spring, and can be used to assist the movement into the upper position.
U.S. Pat. No. 4,712,653, which is incorporated by reference herein, discloses an energy-recycling scissors lift including a platform, a base and a pair of scissors linkages, each having a pair of first and second scissors legs. A bridge structure connects each of the second legs together. A sealed gas cylinder, attached to the base and the bridge structure, moves the platform to an extended position above the base. Energy is stored in the sealed gas cylinder as the platform descends to a retracted position and a compensation device is attached to the scissors lift to compensate for the overforce caused by the sealed gas cylinder.
A weight adjustment mechanism is used which includes means for adjusting the forcing-point radius, i.e the radius of the mounting point of the sealed air cylinder to the bridge structure with regard to the mounting point of the scissors legs at the base, to compensate for and dissipate an amount of overforce imparted by the sealed gas cylinder. Therefore, the weight adjustment mechanism can be used to fine tune a sufficient force that maintains the platform in its extended position, resulting in a scissors lift which can be easily started down to its retracted position. The weight adjustment mechanism can also adjust the upward force needed to start the platform towards its extended position.
The above-referenced patent has the disadvantage that the force applied to the platform in its retracted position can not be adjusted independently from the force applied to the platform in its extended position and vice versa.
FIG. 1 shows a prior art device 1 for lifting a platform 2. The device 1 comprises a scissors-type linkage 4, which includes a first scissors leg 6 and a second scissors leg 8 which are connected at a pivot point 10. A second pair of scissors legs in addition connects the platform 2 and a base 16 but it is not shown for purposes of clarity. FIG. 1 shows the scissors-type linkage 4 in a closed position or closed mode. The first scissors leg 6 is mounted with one end to the platform 2 at a mounting point 12 whereas the other end is movingly supported by a roll 14. The second scissors leg 8 is mounted with one end to the base 16 at a mounting point 18 whereas the other end is movingly supported by a roll 20. The device 1 further comprises a gas spring 22 having a cylinder 24 and a piston rod 26. The gas spring 22 is mounted with one end to the scissor type linkage 4 at a first mounting point 28 and with the other end at a second mounting point 30 to a mounting plate 32 of the base 16.
The gas spring 22 applies a force 34 to the platform 2 which assists the lifting of the platform 2. If an operator grips the platform at a handle 36 and pulls or pushes the platform up, he only has to apply an additional force to the platform so that the sum of the force applied by the gas spring 22 and the force applied by himself exceeds the gravitational force on the platform 2 and lifting device 1.
FIG. 2 shows the prior art device 1 for lifting the platform 2, in which the platform 2 is in an upper position and the scissors-type linkage 4 is in an open position or open mode. The gas spring 22 applies a force 134 to the platform 2 which maintains the platform 2 in the upper position, i.e. the force 134 must be equal to or can be greater than the gravitational force on the platform and the lifting device 1. Advantageously the force 134 exceeds the gravitational force only minimal.
As can be seen from FIGS. 1 and 2 the second mounting point 30 of the gas spring 22 does not move because it is fixed at the mounting plate 32 of the base 16. Therefore, the force 134 is smaller than the force 34 as indicated by the respective length of the arrows 34 and 134. The force applied to the scissors-type linkage 4 and subsequently to the platform 2 by the gas spring 22 depends on the angle between the piston rod 26 and the first scissors leg 6 and it depends on the compression of the gas spring.
Both positions of the platform 2, the upper shown in FIG. 2 and the lower position shown in FIG. 1, can be fixed by the use of a fixing element such as a pin.
An object of the present invention is to provide a method and device for adjusting a first force applied to a movable element in a first position so that a second force applied to the movable element remains constant.
It is a further alternate or additional object of the present invention to provide a method and device for independently adjusting a first and a second force applied to a movable element such as a platform.
The terms xe2x80x9cfirst forcexe2x80x9d, xe2x80x9csecond forcexe2x80x9d, xe2x80x9cthird forcexe2x80x9d and xe2x80x9cfourth forcexe2x80x9d in this application are used herein solely to distinguish the forces from one another, and are not meant to have any other specific meaning.
The present invention provides a method for adjusting a first force applied to a movable element in a first position of the movable element by a force applying device, the force applying device applying a second force to the movable element in a second position of the movable element, comprising the steps of:
connecting the movable element and a base element with a scissors-type linkage;
mounting the force applying device to the scissors-type linkage at a first mounting point;
mounting the force applying device to the base element at a second mounting point;
moving at least one of the first and the second mounting points along a constant force curve, so that the second force remains constant as the first force is adjusted.
The terms xe2x80x9cfirst mounting pointxe2x80x9d, xe2x80x9csecond mounting pointxe2x80x9d, xe2x80x9cthird mounting pointxe2x80x9d and xe2x80x9cfourth mounting pointxe2x80x9d in this application are used herein solely to distinguish the mounting point from one another, and are not meant to have any other specific meaning.
The method according to the invention advantageously allows for compensating for force applying device wear or deviations in strength as it is supplied by the manufacturer, e.g. gas spring wear or deviation. Further, the method according to the invention allows the operators to easily adjust the required force, e.g. a lifting force, to their own liking, preference or need.
According to the invention the method may further comprise the steps of:
providing a further force applying device, the further force applying device applying a third force to the movable element in the first position of the movable element and the further force applying device applying a fourth force to the movable element in the second position of the movable element;
mounting the further force applying device to the scissors-type linkage at a third mounting point;
mounting the further force applying device to the base element at a fourth mounting point; and
adjusting the fourth force applied to a movable element in the second position of the movable element by moving at least one of the third and the fourth mounting points along a constant force curve, so that the third force remains constant as the fourth force is adjusted.
Further the moving of at least one of the first, the second, the third and the fourth mounting point may be along an approximated constant force curve.
In another embodiment of the invention a method for independently adjusting a first and a fourth force applied to a platform comprises the steps of:
connecting the platform and a base element with a scissors-type linkage;
mounting a first gas spring to the scissors-type linkage at a first mounting point and mounting the first gas spring to the base element at a second mounting point;
mounting a second gas spring to the scissors-type linkage at a third mounting point and mounting the second gas spring to the base element at a fourth mounting point;
applying the first force to the platform in an upper position and applying a second force to the platform in a lower position using the first gas spring;
applying a third force to the platform in the upper position and applying the fourth force to the platform in the lower position using the second gas spring;
moving at least one of the first and the second mounting points along a constant force curve, so that the second force remains constant as the first force is adjusted; and
moving at least one of the third and the fourth mounting points along a constant force curve, so that the third force remains constant as the fourth force is adjusted.
The present invention also provides a device for adjusting a first force applied to a movable element, comprising:
a movable element;
a base element;
a scissors-type linkage, the scissors-type linkage connecting the base element and the movable element; and
a force applying device applying the first force to the movable element in a first position of the movable element and applying a second force to the movable element in a second position of the movable element;
the force applying device being mounted to the scissors-type linkage at a first mounting point and being mounted to the base element at a second mounting point, at least one of the first and second mounting points being movable along a constant force curve, so that the second force remains constant as the first force is adjusted.
The device according to the invention can be advantageously used to assist the movement of the movable element, e.g. a liftable platform, which movement can be done by hand by an operator. If the platform is moved into an upper position, the operator can climb up onto it or the platform can be used to lift loads or operators.
According to the invention the movable element may be platform, the first position may be an upper position and the second position may be a lower position.
Further, according to the invention the platform may be a liftable working platform of a printing press and the base element may be part of an operation deck of the printing press.
In another embodiment of the present invention the scissors-type linkage may include at least two pairs of scissors legs, each scissors leg being connect at one end to one of the platform and the base element.
The force applying device may be one of a gas spring, a coil spring, an air cylinder, a pneumatic cylinder or a hydraulic cylinder.
A device according to the invention may further comprise means for moving one of the first and second mounting points along the constant force curve. This means for moving one of the first and second mounting points may include a mounting element movable along a curved slot.
According to the invention the curved slot may approximate the constant second force curve or may be a straight slot.
In a further embodiment of the invention the second mounting point may include a mounting plate pivotally mounted to the base element and having a slot with two ends for receiving a pin, the two ends and the pin limiting the pivotal movement of the mounting plate and the force applying device may be pivotally mounted to the mounting plate.
The present invention further provides a device for adjusting a first force applied to a movable platform of a printing press, comprising:
a base element being part of an operation deck of the printing press;
a scissors-type linkage, the scissors-type linkage connecting the base element and the movable platform, the scissors-type linkage including at least two pairs of scissors legs; and
a gas spring applying the first force to the movable platform in an upper position of the movable platform and applying a second force to the movable platform in a lower position of the movable platform;
the gas spring being mounted to the scissors-type linkage at a first mounting point and being mounted to the base element at a second mounting point, the second mounting point being movable along a constant force curve, so that the second force remains constant as the first force is adjusted.
The device according to the invention may also comprise a further force applying device, the further force applying device applying a third force to the movable element in the first position of the movable element and the further force applying device applying a fourth force to the movable element in the second position of the movable element, the further force applying device being mounted to the scissors-type linkage at a third mounting point and being mounted to the base element at a fourth mounting point. At least one of the third and fourth mounting points may be movable along a constant force curve, so that the third force remains constant as the fourth force is adjusted.